1. Field of the Invention
The present invention relates to a method of production of a dielectric ceramic composition used, for example, as a dielectric layer of a multilayer ceramic capacitor.
2. Description of the Related Art
The dielectric ceramic composition constituting the dielectric layer of the multilayer capacitor as an example of an electronic component is constituted by including various dielectric oxides such as BaTiO3 which is a ferroelectric, or SrTiO3, CaTiO3, CaSrZrO3, CaZrO3, SrZrO3, TiO2, NdTiO3 which are paraelectrics.
The dielectric ceramic composition was normally added with, besides the above dielectric oxides as a main component, a sintering aid to facilitate sintering characteristics, and then fired at high temperature such as 1300° C. or higher.
However, following problems occurs when the firing temperature is high.
First, the temperature becomes higher than the melting point of a base metal such as Ni as a material of an internal electrode, or it may become a temperature range near that. As a result, a melting and a spheroidizing of the base metal particle which is fired together with the dielectric ceramic composition are promoted, and a line characteristic of the internal electrode layer is deteriorated. That is, it may be a factor to cause problem such as the break produced in the internal electrode layer. If the line characteristic of the internal electrode layer deteriorates, the specific permittivity of the obtained capacitor declines, resulting in the decline of a capacitance, and ultimately it cannot manage to obtain a larger capacity and to make the layer thinner.
Second, a firing furnace itself is expensive, and in addition to this, because the deterioration of the used firing furnace becomes prominent, the maintenance and the management cost of the firing furnace increases as the time of use, and along with that the energy cost used for the firing becomes extremely expensive.
Also, because the firing is performed at a high temperature, the particle diameter is difficult to be controlled which easily cause a particle growth of the dielectric oxide particles. As a result, the number of the dielectric particle in the thickness direction of the dielectric layer becomes fewer, and the reliability of the electronic component declines. Furthermore, due to the difference of a thermal expansion coefficient between the dielectric layer and the electrode layer, in some cases the dielectric layers cracked during the firing or the cooling.
Due to such reasons, the firing temperature is preferably made as low as possible.
On the other hand, if the firing temperature is made too low, the dielectric layer cannot be densified, thus the dielectric ceramic composition having sufficient characteristics cannot be obtained. Therefore, it is demanded to fire at even lower temperature without deteriorating the densification of the dielectric ceramic composition.
Patent document 1 discloses a method of production of the dielectric ceramic composition, aiming to produce dielectric ceramic composition under low temperature firing, said method is to produce the dielectric ceramic composition comprising;    a dielectric oxide expressed by a composition formula of [(CaxSr1-x)O]m[(TiyZr1-y-zHfz)O2] (x, y, z, and m in the formula of are; 0.5≦x≦1.0, 0.01≦y≦0.10, 0<z≦0.20 and 0.90≦m≦1.04 respectively),    manganese oxide,    aluminum oxide, and    a sintering aid; wherein    said method of production of dielectric ceramic composition uses the sintering aid comprising;    a first glass composition having SiO2 as a main component,    and further including MO (note that, M is at least one selected from Ba, Ca, Sr and Mg), and    a second glass composition constituted by including B2O3, Al2O3, ZnO and SiO2, having an average particle diameter of 1.5 μm or less.    [Patent document 1] Japanese Unexamined Patent 2005-179105